There is a strong relationship between continued industrialization coupled with economic growth and an increase in the demand for oil, especially for the fuel. The demand for crude oil has exceeded the existing production in India and over and above has been demanding more imports, thereby increasing the reliance on those countries that supply oil. The existing conventional oil production technologies are able to recover only about one-third of the oil originally in place in a reservoir.
Crude oil in oil wells, the original oil in place (OOIP), is present in the oil formation rock which may be carbonate or sand stone. The OOIP is generally pushed up on to the ground with the existing overpressures as primary recovery process. The pressure in the oil well drops with the time and there is a need to create overpressure with other means like water injection or non-inflammable gas for secondary recovery of the OOIP. The choice of a specific secondary recovery technique depends on the specifics of the hydrocarbon accumulation. Water injection or waterflooding is the most common secondary recovery technique. In waterflooding, pressurized water is injected into the oil-bearing formation rock and oil is displaced by water and thus oil is recovered from neighboring crude oil producing oil wells. First crude oil, and subsequently crude oil and water are recovered from the production oil well. The remaining oil in place is enormously large in quantity and a suitable tertiary method of its recovery is the need of hour. However, even after secondary recovery, a significant portion of crude oil (more than 60%) remains in the formation, in some cases up to 75% of the original crude oil in place. The fraction of unrecoverable crude oil is typically highest for heavy oils, tar, and complex formations. In large oil fields, more than a billion barrels of oil can be left after conventional water flooding into oil wells. Much of this remaining oil is in micro-traps due to capillary forces or adsorbed onto mineral surfaces (irreducible oil saturation) as well as bypassed oil within the rock formation. A good number of tertiary recovery processes have been proposed.
Recovery of oil by reducing the viscosity and increasing the overpressures of the oil well is one approach to increase the mobility of oil and there by enhance the oil recovery. In yet another approach, the water with pressure will have increased sweep efficiency due to reduced surface tension in the presence of alkline medium or surfactants. In situ combustion of oil/gas present in the well by pumping oxygen or air, however the concept of the in situ combustion does not result a uniform pressurization and mobilization of the oil. One enhanced oil recovery technique uses microorganisms such as bacteria to dislodge the micro-trapped or adsorbed oil from the rock. The goal of this technique, which is known as microbial enhanced oil recovery (MEOR), is to increase oil recovery of the original subsurface hydrocarbons. MEOR processes typically use microorganisms to: (1) alter the permeability of the subterranean formation, (2) produce biosurfactants which decrease surface and interfacial tensions, (3) mediate changes in wettability, (4) produce polymers which facilitate mobility of petroleum, (5) produce low molecular weight acids which cause rock dissolution, and (6) generate gases (predominantly CO2) that increase formation pressure and reduce oil viscosity. Of all, microbial enhanced oil recovery (MEOR) is presently the most preferred approach, where the use of microorganisms such as bacteria produces certain metabolic products that alter the oil properties and thus facilitate to dislodge the oil adhering to the formation rock. Numerous microorganisms have been proposed for achieving various microbial objectives in subterranean formations. Most MEOR techniques involve injection and establishment of an exogenous microbial population into the oil-bearing formation. The population is supplied with nutrients and mineral salts as additives to the water flood used for secondary oil recovery. The development of exogenous microorganisms has been limited by the conditions that prevail in the formation. Physical constraints, such as the small and variable formation pore sizes together with the high temperature, salinity and pressure of fluids in the formation and the low concentration of oxygen in the formation waters severely limit the types and number of microorganisms that can be injected and thrive in the formation. Biological constraints, such as competition from indigenous microbes and the stress of changing environments (from surface to subsurface) also act to limit the viability of exogenous microorganisms. To overcome these problems, indigenous microorganisms, commonly anaerobic, have been proposed in MEOR projects.
There are bacterial systems like the one described in U.S. Pat. No. 2,907,389 uses oil as a carbon source to produce biosurfactants in the presence of oxygen. The oil shale when pumped as oil bearing rock aqueous slurry and treated thus. However this is used in the case of unconsolidated rock formations only. There aerobic and anaerobic categories in MEOR methods. Aerobic system of MEOR as described in U.S. Pat. No. 3,332,487 and anaerobic bacterial system as described in WO 89/10463 and mix of aerobic and anaerobic bacterial system as described in U.S. Pat. No. 5,492,828.
The oil information normally is under anaerobic conditions and the anaerobic bacterial strains will be there as endogenous microbes that may be of useful for facilitating the oil recovery. A the same time exogenously added microorganisms that can use oil as sole source of carbon or that may be requiring a carbon source for growth as described in U.S. Pat. No. 5,492,828 where mixed cultures of aerobic anaerobic bacteria which use crude oil as sole source of carbon source were used for enhanced oil recovery.
New technologies for recovering this residual oil offers the most timely and cost effective solution to reverse the decline in domestic oil production and to increase the oil reserves of the state. Microbial based oil recovery process is one of such methodologies and has several unique advantages that make it an economically attractive alternative to other processes for enhanced oil recovery. This process does not consume large amounts of energy, as do thermal recovery processes and they do not depend on the price of crude oil, as is the case with many chemical recovery processes. Because microbial growth occurs at exponential rates, it should be possible to produce large amounts of useful products quickly from inexpensive and renewable resources. Economic analysis of some MEOR (Microbial Enhanced Oil Recovery) field trials showed that MEOR based oil recovery has produced oil for as little as three dollars per barrel [Knapp et al., 1992; Bryant et al. 1993].
The MEOR processes can be categorized into three main domains depending on the type of production problem and where the process occurs in the reservoir [Jenneman, 1998]. The much talked-about well bore clean out processes involve the use of hydrocarbon-degrading or scale-removing bacteria to remove deposits from tubing, rods, and other surfaces in the well and thereby avoiding frequent chemical treatments to maintain oil production. It greatly reduces operating costs and extends the lifetime of the well [Raiders et al. 1989]. This approach is a mature commercial technology with thousands of wells treated on a regular basis [McInerney et al. 1985; Nelson and Schneider, 1993). The next MEOR technology is well stimulation where an oil well close to its economic limit is treated with a mixture of anaerobic bacteria and a fermentable carbohydrate, usually molasses [Hitzman, 1983]. The production of acids, solvents, and gases in the well bore region is believed to alter the oil/rock characteristics and improve the drainage of oil into the well.
Microbial enhanced water flooding processes are done late in the course of a water flood and involve the injection of nutrients and or microorganisms into the reservoir in order to stimulate microbial activity throughout the reservoir. In carbonate formations, the production of organic acids by the microbial fermentation of carbohydrates is believed to alter pore structure due to the dissolution of the carbonate minerals and substantial improvements in oil production have been reported with this process [Knapp et al., 1992; Wagner et al., 1995]. A method of microbial enhanced oil recovery using oil as sole source of carbon for the enhancing endogenous biomass using specific nutrients, wherein the biomass thus produced will dissociate the oil from the rock, was described in Patent application No WO 01/33040 A1. In sandstone formations, substantial increase in oil production require that the interfacial tension between the oil and water phases be reduced by a factor of 10,000 or more in order to release the oil that is entrapped in small pores by capillary pressure. The lipopeptide biosurfactant produced by Bacillus licheniformis strain JF-2 substantially reduces the interfacial tension between oil and water [Lazar et al., 1993; Lin et al., 1994]. The introduction of this organism along with other anaerobic bacteria in two field trials in Oklahoma has increased oil production and decreased the water to oil ratio of the produced fluids [Bryant et al., 1993]. The addition of nitrate and/or inhibitors of sulfate reduction to injection waters are also used to control hydrogen sulfide production and improve oil recovery [Telang et al., 1997; Streeb and Brown, 1992].
In addition to the above approaches, a microbial plugging process to reduce permeability variation in oil reservoirs in order to improve the performance of water flood was developed [McInerney et al., 1990; McInerney et al., 1999]. The injection water preferentially flows through the most permeable layers of the rock with little or no movement in the less permeable regions. The oil present in the low permeable regions is by-passed and unrecovered. The stimulation of the growth of indigenous microorganisms in the high permeability regions by nutrient injection reduces water movement in these regions and diverts fluid flow into the less permeable regions of the reservoir that have high oil saturation. Laboratory experiments have shown that in situ microbial growth substantially reduces the permeability of sandstone cores, that microbial growth occurs preferentially in the high permeability regions, and that plugging of the high permeability regions diverts fluid flow into less permeable regions [Portwood, 1995; Raiders et al., 1986]. The invention is related to a bacteria and its use in a Microbial Enhanced Oil Recovery (MEOR) process. Bacteria are injected downhole in a petroleum reservoir to modify its profile. This bacterium has the capability to plug the zones of higher permeability within the reservoir so that a subsequent waterflood may selectively enter the oil bearing less permeable zones. The injected water is used to drive this oil to an area where it may then be recovered as described in U.S. Pat. No. 4,799,545. Since the process does not require the production of a specific chemical or the growth of a specific organism, it should be applicable in many reservoirs.
MEOR methods take advantage of the ability of microbes to produce products for improving oil recovery as described in U.S. Pat. No. 4,971,151 where endogenous populations are increased suitable non-glucose containing carbon source which enhances the surface active properties of the endogenous cultures. These products, in turn, can change oil/rock properties in a positive direction, and thus facilitate additional oil recovery. To be successful, microbes must be able to live and proliferate to the expected level in the harsh reservoir environment. In natural conditions the non-conducive and nutrient limiting conditions play a very important role in keeping the ecological balances of the population system. To stimulate the successions of desirable organisms there is need to modify such environments through introduction of specific and selective nutrients or to introduce the desirable populations or through suppression of non-desirable populations. In any of these cases the criteria to be followed, of course with certain exceptions, would be (1) salinity less than 15% NaCl; (2) temperature less than 180° F.; (3) depth less than 8,000 ft; (4) trace elements (As, Se, Ni, Hg) less than 10-15 ppm; (5) permeability greater than 50 md; (6) oil gravity greater than 15° API; and (7) residual oil saturation greater than 25%. There are many inventions on the MEOR technology using either aerobic or anaerobic or a mixture of both, however, a microbial consortium to work under the conditions stated above has not been reported yet.
In the earlier MEOR methods, the microorganism(s) could not survive at a temperature beyond 70° C. The above draw back was overcome by providing a unique combination of novel indigenous micro-organisms and specifically designed nutrient media along with gradual adaptation of the microbes to the required temperatures in the oil wells. The micro-organism(s) were found to be highly active even at 90° C. The medium supports the growth and proliferation of the culture in extreme conditions. The metabolic products produced by consuming these nutrients protect the microbes. The composition of the nutrients also promotes selectively the bacterial growth of the consortium of the present invention. In addition, the use of formation water provides appropriate concentration of salts in the nutrient medium and the absence of anaerobic bacteria which are harmful to oil reservoirs is avoided. Also, formation water used is compatible with oil reservoir and helps in the growth of multi bacterial strain or consortia of the present invention.